1. Field of the Invention
This invention relates to novel catalysts useful in the preparation of unsaturated organic esters from olefinic compounds, oxygen, and carboxylic acids and to processes for using these catalysts.
2. Description of Related Art
A number of processes for preparing unsaturated organic esters are well known to those in art. The predominant industrial use of such processes is for the preparation of vinyl acetate. Processes for preparing vinyl acetate include, for example, U.S. Pat. No. 3,346,624 which describes a liquid phase process for the oxidation of ethylene to vinyl acetate and acetaldehyde by contacting ethylene with oxygen in a reaction medium comprising a carboxylic acid in the presence of a platinum group metal salt and a redox agent such as chlorides of copper. The redox agent functions as an oxidant to keep palladium in the oxidized state and prevent the palladium from precipitating out of solution and thus becoming inactive for the process.
British patent 976,613 describes the reaction of an unsaturated organic compound, a carboxylic organic acid, oxygen or an oxygen containing gas in the gas phase in the presence of a group VIII noble metal catalyst to form the corresponding ester. The catalyst may be unsupported or supported on a material such as carbon, silica or alumina and may contain 1:10 equivalent per equivalent of catalyst of a metal halide promoter such as cooper chloride.
British patent 1,521,652 describes a catalyst for making vinyl acetate in the gaseous phase from ethylene, oxygen and acetic acid. This patent describes catalysts in the form of particles, each particle comprising a mixture of palladium and gold as noble metals and a support material and having (a) an outer layer of low or zero noble metal content, (b) an inner shell rich in noble metal and (c) a core having low or zero noble metal content.
U.S. Pat. No. 4,048,096 describes a palladium-gold catalyst for the production of vinyl esters such as vinyl acetate by the vapor phase reaction of ethylene, oxygen and a carboxylic acid. Described is a catalyst prepared by impregnating a catalyst support with aqueous solution of water soluble palladium and gold compounds, precipitating water insoluble palladium and gold compounds onto the catalyst support by contacting the impregnated catalyst support with a solution of compounds capable of reacting with the water soluble palladium and gold compounds to form water insoluble palladium and gold compounds (e.g., sodium silicates), converting the water insoluble palladium and gold compounds into palladium and gold metal by treatment with a reducing agent, washing the catalyst with water, and contacting the catalyst with alkali metal acetate and drying the catalyst.
U.S. Pat. No. 4,119,567 describes a supported catalyst composition for the preparation of unsaturated organic esters by the vapor phase reaction of an olefinic compound, oxygen and a lower carboxylic acid; the catalyst containing a Group VIII noble metal. Described is an alumina carrier having an alumina content greater than 99%, a crystalline alpha-alumina content of greater than 96%, a theta-alumina content of less than about 3%, a total calcium and magnesium content of less than 750 ppm, a surface area of about 2 to 6m.sup.2 /g, an average crush strength of from about 20 to 45 lbs., a bulk density of less than about 1.35 g/cc, and an acetic acid loading of less than about 1.5% in 200 hrs. The catalyst is also described as generally containing an alkali metal carboxylate activator and optionally a metal such as gold and copper.
U.S. Pat. No. 3,743,607 describes a catalyst for the catalytic, vapor phase production of vinyl acetate from ethylene, acetic acid and molecular oxygen. Described is a catalyst comprised of palladium and an alkyl metal acetate or formate supported on a carrier and is activated by including metallic gold therein.
There is still a need, however, for catalysts and processes for the production of unsaturated organic esters such as vinyl acetate which provide improved activity and selectivity.